Detection of channel saturation in phase-array ultrasonic non-destructive testing

ABSTRACT

The present invention relates to a method of detecting non-linear operation of a measuring device comprising an array of transducers and at least one receiver channel portion. The method comprises receiving measured signals through transducers of the array, processing the measured signals from the transducers through the receiver channel portion, combining the processed measured signals to produce a combined measurement signal, and detecting non-linearity of the combined measurement signal and non-linear operation of the measuring device by detecting saturation of the receiver channel portion. In one embodiment, the receiver channel portion comprises an analog-to-digital converter, a threshold is assigned to a digital output of the analog-to-digital converter, and saturation of the receiver channel portion is detected when the digital output of the analog-to-digital converter oversteps the assigned threshold. In one application of the invention, the measuring device is a non-destructive testing device.

This application claims the benefit of U.S. Provisional Application No.60/651,983, filed Feb. 14, 2005, the entire contents of which areincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to the detection of non-linearity in ameasuring apparatus.

BACKGROUND OF THE INVENTION

Generally speaking, linearity is an essential feature of an accuratemeasuring apparatus. More specifically, when a signal detected by ameasuring apparatus is amplified by a certain gain, the amplified outputsignal must be proportional to the detected signal. If thisproportionality is not respected and no correction is made, theresulting signal is likely to be erroneous and lead to wrongfulinterpretation.

In the area of non-destructive testing (NDT) of materials andstructures, a so-called “phase array” ultrasonic technique uses nchannels including, for example, an array of n ultrasonic transducers.The n ultrasonic transducers are excited according to a given focal lawdelay profile to ultrasonically scan the tested material or structure.Echoes from defects or flaws present in the tested material or structureare detected by the n ultrasonic transducers to produce correspondingseparate channel signals. An average of the channel signals iscalculated prior to processing thereof.

Those of ordinary skill in the art will appreciate that saturation of atleast one of the n channels will cause non-linearity of the measuringapparatus. More specifically, the calculated average will be erroneousand not representative of the reality.

SUMMARY OF THE INVENTION

To overcome the above discussed problem, the present invention relates,according to a first aspect, to a method of detecting non-linearoperation of a measuring device comprising an array of transducers andat least one receiver channel portion. This method comprises receivingmeasured signals through transducers of the array, processing themeasured signals from the transducers through said at least one receiverchannel portion, combining the processed measured signals to produce acombined measurement signal, and detecting non-linearity of the combinedmeasurement signal and non-linear operation of the measuring device bydetecting saturation of said at least one receiver channel portion.

According to a second aspect, the present invention relates to a methodof detecting non-linear operation of a measuring device comprising anarray of n transducers and a number of n receiver channel portionsrespectively associated to the n transducers. This method comprisesreceiving measured signals through the n transducers, processing themeasured signals from the n transducers through the corresponding nreceiver channel portions, combining the processed measured signals toproduce a combined measurement signal, and detecting non-linearity ofthe combined measurement signal and non-linear operation of themeasuring device by detecting saturation of at least one of the receiverchannel portions.

According to a third aspect, the present invention relates to a methodof detecting non-linear operation of a measuring device comprising anarray of transducers and at least one receiver channel portioncomprising an analog-to-digital converter. The method comprisesassigning a threshold to a digital output of the analog-to-digitalconverter, receiving measured signals through transducers of the array,processing the measured signals from the transducers through said atleast one receiver channel portion, and detecting non-linear operationof the measuring device by detecting saturation of said at least onereceiver channel portion when the digital output of theanalog-to-digital converter oversteps the assigned threshold.

According to a fourth aspect, the present invention relates to a methodof detecting non-linear operation of a measuring device comprising anarray of n transducers and a number of n receiver channel portionsrespectively associated to the n transducers and each comprising ananalog-to-digital converter. This method comprises assigning a thresholdto a digital output of the analog-to-digital converters, receivingmeasured signals through the n transducers, processing the measuredsignals from the n transducers through the n receiver channel portions,respectively, and detecting non-linear operation of the measuring deviceby detecting saturation of at least one of the receiver channel portionswhen the digital output of the corresponding analog-to-digital converteroversteps the assigned threshold.

According to a fifth aspect, the present invention relates to a methodof non-destructive testing of a material or structure using an array ofultrasonic transducers, comprising generating signals supplied toultrasonic transducers of the array to produce ultrasonic wavespropagating through the material or structure, receiving echoes of theultrasonic waves through ultrasonic transducers of the array to produceecho signals, processing the echo signals through at least one receiverchannel portion and combining the processed echo signals to produce acombined measurement signal; and detecting non-linearity of the combinedmeasurement signal by detecting saturation of said at least one receiverchannel portion.

According to a sixth aspect, the present invention relates to a devicefor detecting non-linear operation of a measuring device comprising anarray of transducers. This device comprises at least one receiverchannel portion so configured as to receive measured signals throughtransducers of the array and to process the measured signals from thetransducers, a combiner of the processed measured signals to produce acombined measurement signal, and a detector of saturation of said atleast one receiver channel portion, detection of saturation of said atleast one receiver portion indicating non-linearity of the combinedmeasurement signal and non-linear operation of the measuring device.

According to a seventh aspect, the present invention relates to a devicefor detecting non-linear operation of a measuring device comprising anarray of n transducers. This device comprises: a number of n receiverchannel portions respectively associated to the n transducers, the nreceiver channel portions being so configured as to receive measuredsignals through the n transducers, respectively, and to process themeasured signals from the transducers; a combiner of the processedmeasured signals to produce a combined measurement signal; and adetector of saturation of at least one of the n receiver channelportions, detection of saturation of said at least one receiver channelportion indicating non-linearity of the combined measurement signal andnon-linear operation of the measuring device.

According to an eighth aspect, the present invention relates to a devicefor detecting non-linear operation of a measuring device comprising anarray of transducers. This device comprises: at least one receiverchannel portion comprising an analog-to-digital converter, a thresholdbeing assigned to a digital output of the analog-to-digital converter,and said at least one receiver channel portion being so configured as toreceive measured signals through transducers of the array and to processthe measured signals from the transducers; and a detector of saturationof said at least one receiver channel portion when the digital output ofthe analog-to-digital converter oversteps the assigned threshold,detection of saturation of said at least one receiver channel portionbeing indicative of non-linear operation of the measuring device.

According to a ninth aspect, the present invention relates to a devicefor detecting non-linear operation of a measuring device comprising anarray of n transducers. This device comprises: a number of n receiverchannel portions respectively associated to the n transducers and eachcomprising an analog-to-digital converter, wherein a threshold isassigned to a digital output of the analog-to-digital converter, andwherein said n receiver channel portions are so configured as to receivemeasured signals through the n transducers, respectively, and to processthe measured signals from the transducers; and a detector of saturationof at least one of the receiver channel portions when the digital outputof the analog-to-digital converter of said one receiver channel portionoversteps the assigned threshold, detection of saturation of said atleast one receiver channel portion being indicative of non-linearoperation of the measuring device.

According to a tenth aspect, the present invention relates to a devicefor non-destructive testing of a material or structure using an array ofultrasonic transducers, comprising: a plurality of channels connected toultrasonic transducers of the array, said plurality of channels defininggenerators of signals supplied to the ultrasonic transducers to produceultrasonic waves propagating through the material or structure; at leastone receiver channel portion so configured as to receive echoes of saidultrasonic waves through ultrasonic transducers of the array to produceecho signals and to process the echo signals; a combiner of theprocessed echo signals to produce a combined measurement signal; and adetector of saturation of said at least one receiver channel portion,detection of saturation of said at least one receiver channel portionindicating non-linearity of the combined measurement signal.

The foregoing and other objects, advantages and features of the presentinvention will become more apparent upon reading of the followingnon-restrictive description of an illustrative embodiment thereof, givenby way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a schematic block diagram of a non-restrictive illustrativeembodiment of a phase-array ultrasonic non-destructive testing apparatususing n channels;

FIG. 2 is a schematic block diagram showing an example of averaging ofthe signals from six (6) different channels of the phase-arrayultrasonic non-destructive testing apparatus; and

FIG. 3 is a graph showing the amplitude of an average of the six (6) A/D(analog-to-digital) output channels of FIG. 2 in relation to a percentincrease of receiver input signal level.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

FIG. 1 is a schematic block diagram of a non-limitative example ofphase-array ultrasonic non-destructive testing apparatus 100. Althoughthe present invention will be described in relation to a non-limitativeexample of phase-array ultrasonic non-destructive testing apparatus, itshould be kept in mind that the present invention can also be used inconnection with other types of measuring apparatuses.

As shown in FIG. 1, the phase-array ultrasonic non-destructive testingapparatus 100 comprises an ultrasonic processor 101 associated with adisplay unit 102, for example a LCD (Liquid Crystal Display) display,and a keypad 103, input/output peripherals and/or ports 104 and RS-232USB port 105.

The ultrasonic processor 101 is responsible for system synchronization,signal processing and real-time displaying of the received echo signals.

More specifically, the ultrasonic processor 101 produces synchronizedpulses with pre-programmed width. The synchronized pulses withpre-programmed width are processed through a number of n substantiallyidentical and parallel channels such as 106 respectively associated toultrasonic transducers (not shown), such as piezoelectric elements, ofan ultrasonic phase-array probe (not shown). In one embodiment, thenumber n of channels 106 is equal to the number of ultrasonictransducers of the phase-array probe and each of the n channels 106 isassociated to a respective single one of the n ultrasonic transducersfor supplying and receiving signals to and from this transducer.According to an alternative, each channel 106 is associated to:

-   -   a first ultrasonic transducer supplied with signals from the        channel 106 to produce ultrasonic waves propagating through the        material or structure to be investigated; and    -   a second ultrasonic transducer to detect echoes produced by        reflection of ultrasonic waves on boundaries, defects or flaws        in the investigated material or structure and to produce        corresponding echo signals supplied to the associated channel        106.

The synchronized pulses with pre-programmed width are supplied to adelay circuit 107 of each channel 106. The function of the delay circuit107 is to delay the pulses from the ultrasonic processor 101 in order tosupply to the corresponding ultrasonic transducer the pulses with a timedelay corresponding to the delay associated to this transducer in acorresponding, pre-calculated focal law delay profile.

The delayed pulses from delay circuit 107 are processed through a pulsewidth modulator 108 for adjusting the width of the pulses as desired orrequired by the intended application, and then amplified by a high powerpulse amplifier 109 prior to being supplied to the correspondingultrasonic transducer connected to a pulser output 110 through, forexample, an ultrasonic cable (not shown). The function of the ultrasonictransducer is to create ultrasonic waves propagating through thematerial or structure to be investigated.

Ultrasonic echoes produced by reflection of ultrasonic waves onboundaries, defects or flaws in the material or structure beinginvestigated are detected by the ultrasonic transducer connected to thereceiver input 111. As indicated in the foregoing description, the sameultrasonic transducer or different ultrasonic transducers can beconnected to the output 110 and input 111. Depending on theconfiguration of the connections and the operation of the phase-arrayultrasonic non-destructive testing apparatus 100, a switch 117 can beactuated to interconnect or disconnect the output 110 and input 111 asrequired. Switch 117 can be operated manually or through the ultrasonicprocessor 101 as required.

The reflected ultrasonic echoes are converted by the ultrasonictransducer into electrical echo signals that are processed by a receiverportion of the channel 106. In one embodiment, a receiver channelportion is provided for each channel 106. It is also within the scope ofthe present invention to provide only one receiver channel portion forall the channels 106 using for example a multiplexer (not shown) forsuccessively connecting the transducers to a single receiver channelportion.

Referring back to FIG. 1, in a receiver channel portion, the echosignals from the ultrasonic transducer are amplified by an amplifier112, filtered in accordance with techniques well known to those ofordinary skill in the art through a filter 113 to remove parasitic orunwanted signal components, and then digitized through ananalog-to-digital (A/D) converter 114. The digitized echo signals fromthe analog-to-digital converter 114 are then delayed by a delay circuit115 using the same focal law delay profile as applied by delay circuit107. A combiner 116 combines, for example sums the digitized and delayedecho signals from all the channels 106 to form a sum that is processedthrough the DSP of the ultrasonic processor 101 to form an average thatis stacked to form, for example, a S-Scan image displayed on the displayunit 102 for interpretation by the operator. The display unit 102 can bea liquid crystal display (LCD) calibrated in units of time, depth ordistance. A multi-color LCD display can also be used to provideinterpretive assistance. Just a word to mention that an advantage ofdisplaying the reflected, digitized, delayed, summed and processed echosignals under the form of a real-time S-Scan image display instead ofonly displaying A-Scan signals, is that the boundaries, flaws or defectsand their positions can be more easily identified on the display unit102. S-Scan images and A-Scan signal are well known to those of ordinaryskill in the art and, for that reason, will not be further described inthe present specification.

Finally the S-Scan images can be stored through the input/output port104 or through the USB port 105. Internal data logging capabilities canalso be provided for to record selected full waveforms and setupinformation associated with each test.

As indicated in the foregoing description, should one of the n channelsbe saturated before the processor 101 calculates the average of thereceived ultrasonic channel signals, this average will be affected, thatis erroneous and not representative of the reality. This situation canbe illustrated in FIG. 2 through a non-limitative example including six(6) channels A, B, C, D, E and F (n=6). In the example of FIG. 2, theaverage S is calculated by the combiner 116/processor 101 using thefollowing relation:S=(A+B+C+D+E+F)/6

In the non-limitative example of FIG. 2, let's consider that the maximumreceiver 111 input signal level is 100% in each channel n beforereaching saturation of that channel. As indicated in the following Table1, let's also determine an initial average adjusted to a value of 40%and a focal law delay profile imposing the following values A=5%, B=50%,C=65%, D=65%, E=50% and F=5%.

More specifically, Table 1 shows values of the average obtained with aconstant increase of receiver 111 input signal level (shown in italic)by steps of the order of 5%. This is made by simply adding at each stepan increase of 5% on each channel n in order to obtain an average withthe same percentage as the receiver 111 input signal level increase.

TABLE 1 Variation of the average as a function of the increase in A/Doutput signal level of each channel Receiver 111 Input Signal Level A/DOutput Signal Level for Each Channel (%) Average (%) A B C D E F (%)  05 50 65 65 50 5 40.00  5 10 55 70 70 55 10 45.00 10 15 60 75 75 60 1550.00 15 20 65 80 80 65 20 55.00 20 25 70 85 85 70 25 60.00 25 30 75 9090 75 30 65.00 30 35 80 95 95 80 35 70.00 35 40 85 100  100  85 40 75.0040 45 90 100  100  90 45 78.33 45 50 95 100  100  95 50 81.67 50 55 100 100  100  100  55 85.00 55 60 100  100  100  100  60 86.67 60 65 100 100  100  100  65 88.33

The graph 300 of FIG. 3 shows that from point 301 of the curve, thecalculated average is no longer proportional to the increase in receiver111 input signal level (non-linear zone 302 in the graph of FIG. 3 andbold portion in Table 1). This situation is met as soon as one of thechannels is saturated. This can be explained as follows: since everysaturated channel n remains at the same A/D output level (100%) and thereceiver 111 input signal level of the other channels n increases by 5%,variation of the average is no longer proportional to the increase inreceiver 111 input signal level.

In the field of medical imaging, such a situation is not critical sincesaturation of one channel will result in an image deformation, forexample a blurred image that can be visually detected on the display.The operator can then adjust the gain of the measuring apparatus inorder to eliminate the image deformation.

In the case of NDT, it is very difficult, even impossible, for theoperator to detect an irregularity, such as saturation of a channel,since the obtained results are not images but channel echo signals. Thisis the incentive for designing a phase-array ultrasonic non-destructivetesting apparatus capable of producing an alarm indicating to theoperator that at least one of the channels n is saturated.

Referring back to FIG. 1, the analog-to-digital converter 114 isdesigned to produce a saturation-indicative signal 118, for example asaturation bit, in response to detection of saturation of thecorresponding channel n. This saturation bit 118 is supplied to theultrasonic processor 101. In response to the saturation bit 118, theultrasonic processor 101 produces an audible alarm and/or a visual alarmdisplayed on the unit 102 to indicate to the operator that at least onechannel is saturated. The selection of an appropriate means forgenerating the alarm in response to the saturation bit 118 is believedto be within the capacity of those of ordinary skill in the art.

For example, the saturation-indicative signal 118 (ADx_OTR) can besimply a logic level 1 produced when the analog-to-digital converter 114is saturated, i.e. when a bit overflow occurs during theanalog-to-digital conversion.

According to a non-limitative alternative embodiment, saturationdetection does not require the production of a saturation-indicativesignal 118 nor a saturation threshold equivalent to the full scaleconversion value of the analog-to-digital converter 114. Morespecifically, the alternative embodiment assigns as saturation thresholdan output conversion value of the analog-to-digital converter 114 lowerthan the full scale conversion value, for example 1111111111 for a10-bit analog-to-digital converter. For example, a threshold value of1111111110 could be used.

According to this alternative embodiment, the digital output of theanalog-to-digital converter 114 is monitored by a digital logic circuit(not shown) that detects the saturation and non-linearity event when thedigital output of the analog-to-digital converter 114 oversteps thethreshold value, for example “1111111110” in the above non-limitativeexample. This digital logic circuit (not shown) then produces an outputsignal representative of the detected saturation and non-linearity eventof the phase-array ultrasonic non-destructive testing apparatus. Whenusing a digital logic circuit according to the alternative embodiment,the ultrasonic processor 101 responds in the same way as describedearlier in response to the saturation-indicative signal 118.

According to another non-limitative alternative embodiment, saturationdetection does not require:

a) the production of a saturation-indicative signal 118, nor

b) a saturation threshold equivalent to the full scale conversion valueof the analog-to-digital converter 114, nor

c) the assignment of a saturation threshold to an output conversionvalue of the analog-to-digital converter 114, nor

d) a digital logic output signal (not shown) resulting from detection ofsaturation event resulting from method c above.

Instead, when one of the stages within the entire signal path of thereceiver channel portion, starting at input 111 and ending at the outputof filter 113, becomes saturated, this event can be detected by theultrasonic processor 101 by comparing the preceding measured echo signallevel of each channel with the current measured echo signal level ofeach channel respectively. Specifically, the preceding and currentmeasurements made for a particular channel are compared to determinewhether the percent increase is the same as the percent increasecalculated for any of the other channels with lower analog-to-digitalconverter 114 output values for the measured echo signals. If thepercent increase is substantially lower than the other channels, thenthe ultrasonic processor 101 detects this condition and produces anoutput signal representative of the detected saturation andnon-linearity event of the phase-array ultrasonic non-destructivetesting apparatus.

In Table 1, the saturation and non-linearity condition is indicated bythe bold numbers.

NON-LIMITATIVE EXAMPLE

The analog-to-digital converter 114 is a 10-bit analog-to-digitalconverter. The saturation-indicative signal 118 is initially equal to 0(ADx_OTR=0). Since the analog-to-digital converter 114 is a 10-bitanalog-to-digital converter, the maximum amplitude of the output digitalsignal is 1111111111. If the result of the analog-to-digital conversionis larger than 1111111111, bit overflow occurs and thesaturation-indicative signal 118 is made equal to 1 (ADx_OTR=1). Inresponse to ADx_OTR=1, a saturation alarm is generated by the ultrasonicprocessor 101 to indicate non-linear operation of the phase-arrayultrasonic non-destructive testing apparatus.

Obviously, detection of the saturation is performed within each of the nchannels 106, in order to ensure that no channel is saturated, or in thesingle receiver channel portion when a multiplexer as describedhereinabove is provided.

Following the saturation alarm, the gain of the receiver channelportion(s) can be manually reduced by an operator or automaticallyreduced by the ultrasonic processor 101 in accordance with apredetermined protocol.

Although the present invention has been described in the foregoingdescription in connection with a non-restrictive illustrative embodimentthereof, numerous modifications to this non-restrictive illustrativeembodiment can be implemented without departing from the scope andnature of the invention. For example, the present invention can beapplied to measuring devices other than a phase-array ultrasonicnon-destructive testing apparatus.

1. A method of detecting non-linear operation of a measuring devicecomprising an array of transducers and at least one receiver channelportion, said method comprising: receiving measured signals throughtransducers of the array; processing the measured signals from thetransducers through said at least one receiver channel portion;combining the processed measured signals to produce a combinedmeasurement signal; detecting non-linearity of the combined measurementsignal and non-linear operation of the measuring device by detectingsaturation of said at least one receiver channel portion, and, producinga saturation-indicative signal.
 2. The method according to claim 1,further comprising triggering an alarm in response to detection ofnon-linearity of the combined measurement signal and non-linearoperation of the measuring device.
 3. The method according to claim 2,further comprising adjusting a gain of said at least one receiverchannel portion in response to triggering of said alarm.
 4. The methodaccording to claim 1, wherein the measuring device is a non-destructivetesting device.
 5. The method according to claim 4, wherein saidtransducers are ultrasonic transducers and said measured signals areultrasonic echo signals.
 6. The method according to claim 5, whereinsaid ultrasonic transducers are piezoelectric transducers.
 7. The methodaccording to claim 1, wherein combining the processed measured signalscomprises calculating an average of the processed measured signals. 8.The method according to claim 1, wherein said at least one receiverchannel portion comprises an analog-to-digital converter and whereindetection of saturation of said at least one receiver channel portioncomprises producing a saturation bit through the analog-to-digitalconverter.
 9. A method of detecting non-linear operation of a measuringdevice comprising an array of n transducers and a number of n receiverchannel portions respectively associated to the n transducers, saidmethod comprising: receiving measured signals through the n transducers;processing the measured signals from the n transducers through thecorresponding n receiver channel portions; combining the processedmeasured signals to produce a combined measurement signal; detectingnon-linearity of the combined measurement signal and non-linearoperation of the measuring device by detecting saturation of at leastone of the n receiver channel portions; and, producing asaturation-indicative signal.
 10. A method of non-destructive testing ofa material or structure using an array of ultrasonic transducers,comprising: generating signals supplied to ultrasonic transducers of thearray to produce ultrasonic waves propagating through the material orstructure; receiving echoes of said ultrasonic waves through ultrasonictransducers of the array to produce echo signals; processing the echosignals through at least one receiver channel portion and combining theprocessed echo signals to produce a combined measurement signal;detecting non-linearity of the combined measurement signal by detectingsaturation of said at least one receiver channel portion; and, producinga saturation-indicative signal.
 11. The method of claim 10, wherein saidat least one receiver channel portion comprises a plurality of receiverchannel portions.
 12. The method of claim 10, wherein the array ofultrasonic transducers comprises a number of n ultrasonic transducers,and wherein said at least one receiver channel portion comprises anumber of n receiver channel portions respectively associated to the nultrasonic transducers.
 13. The method according to claim 10, furthercomprising triggering an alarm in response to detection of non-linearityof the combined measurement signal.
 14. The method according to claim13, further comprising adjusting a gain of said at least one receiverchannel portion in response to triggering of said alarm.
 15. The methodaccording to claim 10, wherein combining the processed echo signalscomprises calculating an average of the processed echo signals.
 16. Themethod according to claim 10, wherein said ultrasonic transducers arepiezoelectric transducers.
 17. The method according to claim 10, whereinsaid at least one receiver channel portion comprises ananalog-to-digital converter and wherein detection of saturation of saidat least one receiver channel portion comprises producing a saturationbit through the analog-to-digital converter.
 18. A device for detectingnon-linear operation of a measuring device comprising an array oftransducers, said device comprising: at least one receiver channelportion so configured as to receive measured signals through transducersof the array and to process the measured signals from the transducers; acombiner of the processed measured signals to produce a combinedmeasurement signal; and a detector of saturation of said at least onereceiver channel portion, detection of saturation of said at least onereceiver portion indicating non-linearity of the combined measurementsignal and non-linear operation of the measuring device, wherein thedetector of saturation comprises a generator of a saturation-indicativesignal.
 19. The device according to claim 18, further comprising analarm triggered in response to detection of saturation of said at leastone receiver channel portion.
 20. The device according to claim 19,further comprising a processor so configured as to adjust a gain of saidat least one receiver channel portion in response to triggering of thealarm.
 21. The device according to claim 18, wherein the measuringdevice is a non-destructive testing device.
 22. The device according toclaim 21, wherein said transducers are ultrasonic transducers and saidmeasured signals are ultrasonic echo signals.
 23. The device accordingto claim 22, wherein said ultrasonic transducers are piezoelectrictransducers.
 24. The device according to claim 18, wherein the combinerof the processed measured signals comprises a calculator of an averageof the processed measured signals.
 25. The device according to claim 18,wherein said at least one receiver channel portion comprises ananalog-to-digital converter and wherein the detector of saturation ofsaid at least one receiver channel portion comprises theanalog-to-digital converter to produce a saturation bit.
 26. A devicefor detecting non-linear operation of a measuring device comprising anarray of n transducers, said device comprising: a number of n receiverchannel portions respectively associated to the n transducers, the nreceiver channel portions being so configured as to receive measuredsignals through the n transducers, respectively, and to process themeasured signals from the transducers; a combiner of the processedmeasured signals to produce a combined measurement signal; and adetector of saturation of at least one of the n receiver channelportions, detection of saturation of said at least one receiver channelportion indicating non-linearity of the combined measurement signal andnon-linear operation of the measuring device, wherein the detector ofsaturation comprises a generator of a saturation-indicative signal. 27.A device for non-destructive testing of a material or structure using anarray of ultrasonic transducers, comprising: a plurality of channelsconnected to ultrasonic transducers of the array, said plurality ofchannels defining generators of signals supplied to the ultrasonictransducers to produce ultrasonic waves propagating through the materialor structure; at least one receiver channel portion so configured as toreceive echoes of said ultrasonic waves through ultrasonic transducersof the array to produce echo signals and to process the echo signals; acombiner of the processed echo signals to produce a combined measurementsignal; and a detector of saturation of said at least one receiverchannel portion, detection of saturation of said at least one receiverchannel portion indicating non-linearity of the combined measurementsignal, wherein the detector of saturation comprises a generator of asaturation-indicative signal.
 28. The device of claim 27, wherein saidat least one receiver channel portion comprises a plurality of receiverchannel portions.
 29. The device of claim 27, wherein the array ofultrasonic transducers comprises a number of n ultrasonic transducers,and wherein said at least one receiver channel portion comprises anumber of n receiver channel portions respectively associated to the nultrasonic transducers.
 30. The device according to claim 27, furthercomprising an alarm triggered in response to detection of saturation ofsaid at least one receiver channel portion.
 31. The device according toclaim 30, further comprising a processor so configured as to adjust again of said at least one receiver channel portion in response totriggering of the alarm.
 32. The device according to claim 27, whereinthe combiner of the processed echo signals comprises a calculator of anaverage of the processed echo signals.
 33. The device according to claim27, wherein said ultrasonic transducers comprise piezoelectrictransducers.
 34. The device according to claim 27, wherein said at leastone receiver channel portion comprises an analog-to-digital converterand wherein the detector of saturation of said at least one receiverchannel portion comprises the analog-to-digital converter to produce asaturation bit.